A vertical transistor with a trench gate structure is applied for a power semiconductor device. The vertical transistor with a trench gate structure has a gate electrode formed in a gate trench provided in a semiconductor layer. Examples of the vertical transistor are a metal oxide field effect transistor (MOSFET) and an insulated gate bipolar transistor (IGBT). Since the gate electrode is provided in the trench, the degree of integration is improved and it is possible to reduce the on-resistance of the vertical transistor.
In the vertical transistor with the trench gate structure, a contact region for contact between a source electrode and a source region may be formed between adjacent gate trenches. When the pitch of the gate trenches is reduced in order to increase the degree of integration of the vertical transistor with the trench gate structure, it is difficult to ensure the amount of overlap between the source region and the source electrode. When the amount of overlap between the source region and the source electrode is reduced, there is a concern that contact resistance will increase and the on-resistance of the vertical transistor will increase.